Preparation and characterization of a highly soluble Aβ1-42 peptide variant

An Efficient Method of Expression and Purification of Amyloid-Beta (Aβ1-42) Peptide from E. coli

Amyloid-beta (Aβ) aggregation into soluble oligomers and fibril formation are associated with Alzheimer's disease (AD) pathogenesis. Aβ_1-42 is the major form of the Aβ peptide present in neuritic plaques and shown to be neurotoxic both in vivo and in vitro. However, understanding the mechanism of its toxicity, aggregation, and other biochemical properties is limited because of its difficult production (recombinant or synthetic) and irreproducibility issues attributed to batch-to-batch preparation differences. Chemically synthetic Aβ_1-42 is now well established, but it always introduces up to 5% D-isomers along with its L-isomeric form, and thus it is not fruitful for biochemical/structural studies. Here, we optimized an efficient published method for expression and purification of Aβ_1-42 upon overexpression in Escherichia coli (E. coli) that provides a satisfactory yield as well as minimizes the variability between batch preparations. With the present protocol, ~7-8 mg/liter of unlabeled peptide and ~3.5-4 mg/liter for ¹³C,¹⁵N-labeled (double-labeled) Aβ_1-42 were obtained.

Biological and methodological complexities of beta-amyloid peptide: Implications for Alzheimer's disease research

Although controversial, the amyloid cascade hypothesis remains central to the Alzheimer's disease (AD) field and posits amyloid-beta (Aβ) as the central factor initiating disease onset. In recent years, there has been an increase in emphasis on studying the role of low molecular weight aggregates, such as oligomers, which are suggested to be more neurotoxic than fibrillary Aβ. Other Aβ isoforms, such as truncated Aβ, have also been implicated in disease. However, developing a clear understanding of AD pathogenesis has been hampered by the complexity of Aβ biochemistry in vitro and in vivo. This review explores factors contributing to the lack of consistency in experimental approaches taken to model Aβ aggregation and toxicity and provides an overview of the different techniques available to analyse Aβ, such as electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, dye-based assays, size exclusion chromatography, mass spectrometry and SDS-PAGE. The review also explores how different types of Aβ can influence Aβ aggregation and toxicity, leading to variation in experimental outcomes, further highlighting the need for standardisation in Aβ preparations and methods used in current research.

Cloning and high-level expression of monomeric human superoxide dismutase 1 (SOD1) and its interaction with pyrimidine analogs

Superoxide dismutase 1 (SOD1) is known to be involved in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS) and is therefore considered to be an important ALS drug target. Identifying potential drug leads that bind to SOD1 and characterizing their interactions by nuclear magnetic resonance (NMR) spectroscopy is complicated by the fact that SOD1 is a homodimer. Creating a monomeric version of SOD1 could alleviate these issues. A specially designed monomeric form of human superoxide dismutase (T2M4SOD1) was cloned into E. coli and its expression significantly enhanced using a number of novel DNA sequence, leader peptide and growth condition optimizations. Uniformly ¹⁵N-labeled T2M4SOD1 was prepared from minimal media using ¹⁵NH₄Cl as the ¹⁵N source. The T2M4SOD1 monomer (both ¹⁵N labeled and unlabeled) was correctly folded as confirmed by ¹H-NMR spectroscopy and active as confirmed by an in-gel enzymatic assay. To demonstrate the utility of this new SOD1 expression system for NMR-based drug screening, eight pyrimidine compounds were tested for binding to T2M4SOD1 by monitoring changes in their ¹H NMR and/or ¹⁹F-NMR spectra. Weak binding to 5-fluorouridine (FUrd) was observed via line broadening, but very minimal spectral changes were seen with uridine, 5-bromouridine or trifluridine. On the other hand, ¹H-NMR spectra of T2M4SOD1 with uracil or three halogenated derivatives of uracil changed dramatically suggesting that the pyrimidine moiety is the crucial binding component of FUrd. Interestingly, no change in tryptophan 32 (Trp32), the putative receptor for FUrd, was detected in the ¹⁵N-NMR spectra of ¹⁵N-T2M4SOD1 when mixed with these uracil analogs. Molecular docking and molecular dynamic (MD) studies indicate that interaction with Trp32 of SOD1 is predicted to be weak and that there was hydrogen bonding with the nearby aspartate (Asp96), potentiating the Trp32-uracil interaction. These studies demonstrate that monomeric T2M4SOD1 can be readily used to explore small molecule interactions via NMR.